Catalase represents a system in Drosophila that demonstrates considerable promise for the successful isolation of a number of different kinds of regulator mutants of a specific genetic locus. The system is novel with respect to other gene-enzyme systems analyzed in Drosophila in that simple but sensitive methods have been developed, using a specific inhibitor, for the direct analysis of rates of synthesis and degradation of the gene product, and that these techniques can be readily applied to an examination of mutations that affect the high and low intensity, time specific, and tissue specific expression of that gene. It is axiomatic that mutations which alter the control of a structural gene locus do so by modulating the rate of synthesis of the final gene product. It then follows that a demonstration of altered synthetic rates is the ultimate illustration of a change in the mechanistic control pattern at some level of the overall process of gene expression. The function of such regulatory genes and their organization in the eukaryotic genome is the principal goal of this research project.